Formaldehyde absorbent composition



United States PatentO 3,400,079 I FORMALDEHYDE ABSORBENT COMPGSITIOILv Alfred T. Clifford, Ware Shoals, and Kenneth C. Hokane son, Greenwood, S.C., assignors to Riegel Textile Corporation, Ware Shoals, S'.C. No Drawing. Continuation-impart of application Ser. No. 337,174, Jan. 13, 1964. This application Dec..12,, 1966, Ser. No. 600,790 j 9 Claims. (Cl. 252-184) ABSTRACT OF THE DISCLOSURE A solid cohesive composition for removingformaldehyde odors from the air comprising an intimate mixture of a water-soluble salt f. sulfurous acid selected from the group consisting of the alkali metal salts and ammonium salts of sulfurous acid, a humectant" in sufficent amount to insure the presence of water in the Composition to maintain the salt partially, insolution, and a solid hydrophilic binder to maintain the intimate mixture cohesive.

This application is a continuation-in-part of our co pending application Ser. No. 337,174, filed Jan. 13, 1964, and now abandoned, as such, relates to a formaldehyde absorbent composition and more particularly to a composition in solid form which will effectively purge objectionable formaldehyde odors from the air.

There has long been a need for an effective means of removing or reducing formaldehyde odors from the air enclosed areas, the released formaldehyde may not be Y objectionable. In closed rooms, however, even'those with 'air conditioners, the formaldehyde released-from these treated fabrics or products may be objectionable oreven toxic.

A Widely accepted standard for measuring the permissible amounts of toxic or odoriferous gases in the air is the so-called Maximum Allowable Concentration (MAC) value. The MAC value is supposed to represent the greatest amount of a contaminating gas to which a person may be continuously exposed without danger'to his health. For formaldehyde gas the MAC value generally agreed upon is five parts per million. For formal dehyde gas, five parts per million is also approximately the lowest amount which canb'e detected by the average person.'Fiftee'n"parts per million is approximately the maximum amount which can be tolerated even for short periods of time by the average person. Thus, a person who could work indefinitely in an atmosphere containing less than five parts per million of formaldehyde gas 'Without detecting a formaldehyde odor would be extremely uncomfortable in an atmosphere containing approximately fifteen parts per million with severe irritation to *the eyes and mucous membranes.

It is therefore a primaryobject of this inventory to previde a satisfactory means to purge the air of formalde-.

hyde gas or reduce the concentration of formaldehyde gas in the air .to a value of less than five-parts per million.

It has-been found by this. invention ,that inexpensive saltsof sulfurous acid in solid compound form may be used to accomplish this object.

'Solutions of the alkali metal (Group I-A of the Periodic Table, and ammonium) salts ofsulfurous acid, normal sulfites, acid sulfites andpyrosulfites- (or meta bisu-lfites) all react with formaldehyde to give a water soluble, stable, nonodorous salt of methylol sulfonic acid, HOCH SO M; M is an alkali metal (Group I-A of the Periodic Table) or ammonium. The exact mechanism of this reaction is not known. For purposes of this invention it is not necessary to know the exact nature of this reactiongit is significant only that it has been found that all salts of sulfurous acid in a water so-lutionreact with formaldehyde to produce a stable, nonodorous compound.

Although it isknown that aqueous solutions of the salts of sulfurous acid react with formaldehyde to produce a chemical compound, the use of such-salts as a commercial absorbent for removing formaldehyde odors from the atmosphere has not been feasible for several reasons. When aqueous solutions of such salts react with formaldehyde at certain pHvalues, the solutions release S0 gas t-o'the atmosphere to produce a distinct obnoxious odor which would preclude the use of such salts in air-purifying system. Additionally, difiiculty of handling and incorporating a liquid material, such as the salt solutions, in the environment in which an absorbent-type airpurifier is most conveniently and often used, e.'g., aircooling, heating and circulating systems, further discourages the use of such salts.

' In accordance with the present invention, we have provided a novel composition of matter which permits the effective use of the salts of sulfurous acid as an absorbent or air-purifier to remove formaldehyde from the atmosphere. More specifically, the present invention provides a cohesive composition containing the salt which can be readily adapted to environments not susceptible to a liquid-type formaldehyde absorbent.

We have discovered that the reactive salts of sulfurous acid need not be in liquid form, as such, in order to react with formaldehyde, but that a small amount of water in intimate mixture with the salts penmits effective absorption of formaldehyde from the air when the air is passed over 'and/ or through the mixture.

In addition, we have found that the formaldehyde-salt reaction,'which produces a salt of methylol sulfonic acid, can be controlled to avoid the release of objectionable by-product odors. Although the foremaldehyde-salt reaction occurs over a wide range of hydrogen ion concentrations, e.g., pH may vary from a pH of 4 when pure sodium pyrosulfite is dissolved in water (in solution often called sodium acid sulfite or sodium bisulfite) to a pH of 9.5 when normal sodium sulfite, Na SO is dissolved in water, by controlling the pH range of the salt solution, the S0 gases released to the atmosphere cannot be detected by the normal human senses so as to be objectionable.

More specifically, we have found that although at a pH of below 5, solutions of the sulfurous acid salts release SO gases to produce a distinct obnoxious odor, at pH values between about 6.5 and 7.0, S0 odor can be detected by only a few persons. At a pH between 7 and 9.5 theodor is not detectable. Therefore, by controlling the pH of the composition of the present invention between the range of about 6.5 to 9.5, the composition does not introduce objectionable detectable S0 vapors into the air during absorption of the formaldehyde.

An alkali metal salt of sulfurous acid, which in water solution gives a pH between 6.5 and 9.5, may be conveniently prepared in three ways, by mixing a pyrosulfite and a normal sulfite, by treating a pyrosulfite with a base, and by treating a normal sulfite with an acid. Within this practical operating pH range of from about 6.5 to 9.5,

optimum results have been obtained when a pH range. of approximately pH 7 to 8 is maintained.

Any of the alkali metal (Group IA of the Periodic Table, and ammonium) salts of sulfurous acid may be used to make the products of this invention. Economic considerations indicate the use of sodium or potassium salts. The commercial grades of the following salts are satisfactory: (1) sodium sulfite, Na SO (2) potassium sulfite, K 50 (3) sodium pyrosulfite, Na S O also called sodium meta bisulfite and sodium bisulfite; (4) potassium pyrosulfite, K S O also called potassium meta bisulfite and potassium bisulfite.

In preparing the solid composition containing the salts of sulfurous acid it is necessary to assure the presence of enough water therein to activate the salts of sulfurous acid. To do so, we provide in intimate mixture with the salt a humectant which operates to attract water from the atmosphere and control the amount of the same in the composition so as to maintain the salts partly in solution and thus free to react with formaldehyde. H

To maintain the humectant and partially solubilized salt mixture together and in solid form, a solid binder material is intimately mixed with the salt and humectant to form a cohesive composition. To permit the humectant to function properly, the binder must be of the type which permits water to freely enter the composition; therefore, hydrophilic or water-soluble binders are preferred. Although any binder which functions as described may be utilized, binders which are commercially available and satisfactory for such purpose are the hydrophilic organic gums, such as hydroxyethyl cellulose, methyl ce1lulose and sodium carboxymethyl cellulose, and the inorganic plastics, such as attapulgite clay, and kaolin. Various mixtures of hydrophilic inorganic and organic binders may also be used.

The humectant is present in the composition not only to provide for the presence of enough water to activate the salts of sulfurous acid, but also to aid in plasticizing the binder during formulation and use of the composition. Any of the variety of known humectants may be used and, by way of example, humectants readily available which have exhibited satisfactory results are glycerol, sorbitol, diethylene glycol, and sodium lignosulfonate.

The exact amounts of the particular ingredients used in the composition are not critical and may be varied, depending on the degree of absorption desired, so long as the pH of the composition is maintained within the ranges specified to avoid the production of detectable obnoxious odors.

The novel solid composition set forth above may be produced in various solid forms, e.g., crumbs, grains, flakes, pellets, fibers, puffs, and spaghetti-like masses or curved rods. This solid salt-binder-hu-mectant-water mixture is preferably prepared in a physical form which exposes relatively large surface areas to the air to provide the best results. It has been found that the pellets, spaghetti-like masses, and flakes are preferable for this purpose.

The following examples are given only to illustrate the manner in which the present invention may be practiced, and are not intended to limit the scope of the invention:

EXAMPLE 1 A viscous dough is prepared by mixing the following ingredients, all parts by weight:

Parts Sodium pyrosulfite 45.0 Sodium hydroxide 9.4 Hydroxyethyl cellulose 9.6 Glycerine 4.8 Water 31.2

The dough is extruded through orfices inch in diameter and collected as soft spaghetti-like masses in a tray. This is transferred to an oven and dried at a temperature of 275 F. The resulting product is a hard, non-friable, resilient solid in spaghetti-like masses with the following composition, all parts by weight:

' Parts Sodium salt of sulfurous acid 75.5 Hydroxyethyl cellulose 13.0 Glycerine 6.5 Water 5 0 EXAMPLE 2 Using the following ingredients, a viscous dough is prepared in a mixing-extruding machine and extruded in folds onto a moving belt, thence through an oven maintained at 250 F., all parts by weight:

Parts Sodium pyrosulfite 15.0 Sodium sulfite 35.0 Glycerine 7.5 Sodium carboxymethyl cellulose 14.2 Water 28.3

The product which emerges from the oven is a hard, resilient solid in spaghetti-like masses with the following approximate composition, all parts by weight:

Parts Sodium salt of sulfurous acid 65.0 Sodium carboxymethyl cellulose 18.5 Glycerine 9.8 Water 6.7

EXAMPLE 3 A dough is prepared as in Example 2 except that the following ingredients are used, all parts by weight:

Parts Sodium sulfite 50.0 Sulfuric acid 6.7 Hydroxyethyl cellulose 9.6 Glycerine 7.5 Water 26.2

When dried to spaghetti-like masses, as in Example 2, the product has the following approximate composition, all parts by weight:

A dough is prepared as in Example 2 except that the followmg ingredients are used, all parts by weight:

Parts Sodium pyrosulfite 40.0 Sodium hydroxide 1 1.1 Commercial sodium lignosulfona-te 7.0 Sodium carboxymethyl cellulose 17.8 Water 28.2

.Scdium pyrosulfite q--. Sodium hydroxide 5.4

The doughis processedasin Example 2. The resulting composition has approximately the following-composition, all parts by weight:

, A doughis prepared-as in Example 2'except that the following ingredients are used, all parts byweightr.

When processed 'as inlE'xarnple 2; the resulting spaghetti-like product has a composition approximately as follows, all parts by weight:

Parts Potassium sulfite 65.0 Sodium carboxymethyl cellulose l. 18.2 Glycerine I 9.8 Water 7.0

A suitable example of the process and ingredients for forming flakes of the composition is as follows:

EXAMPLE 6 A soft paste is prepared by mixing the following ingredients, all parts by weight:

Parts 20.0

sqiumearbbx methy1 cellulose 2.7 Glycerine 7.2 Water 64.7

The paste is dried and flaked on a drum drier. The resulting product in flake form has approximately the following composition, all parts by weight:

Parts Sodium salt of sulfurous acid 67.0 Sodium carboxymethyl cellulose 7.0 Glycerine 19.0 Water 7.0

EXAMPLE 7 A dough is prepared as in Example 2 except that the When dried to spaghetti-like masses, as in Example 2,

the product has, the following approximatecornposition,

ll t b wsisstl.

Parts Potassium salts of sulfurous and sulfuric acids 75.0 Hydroxyethyl-cellulose 10.6 Glycerine 1 v f 1 8.4 Water 6.0

' 9-0 p EXAMPLE 8 p A coarse powder or crumb is prepared by mixing the following ingredients, all parts .by weight: 1

Parts Water soluble hydroxyethyl cellulose 11.2 Water v V, 10.0 Glycerol p 9.5 Sodium sulfite l M ll "58.2 s mpymsume 3 1- Using a water-cooled rubber extruder, the crumb is extruded throughround orifices /3 inch in diameter and collected .on a movable belt in soft, pliable, spaghetti-like masses. These soft, pliable masses are folded between two layers of air filtering material so as to form the inner layer of a three-ply mat. The three-ply mat is cut to pieces of the desired size and framed to form expendable air filters. The air filters may be allowed to dry by exposing to ambient air of low humidity for several days, or they may be dried in an oven. After drying the inner layer of the filters is a tough, resilient, non-friable material 'with the following approximate composition:

Parts .Water soluble hydroxyethyl cellulose 12.0 Water 6.0

Glycerol 10.0 Sodium salts of sulfurous acid 72.0

When the three-ply expendable filters described above are used in air conditioning systems, the outer layers serve to remove solid particles from air and the inner layers serves tqremove .both solid particles and formaldehyde gas. The inner layer will retain its shape and position in the filter even though the filter is subjected to continuous jostling or vibration.

EXAMPLE 9 EXAMPLE 10 A crumb is prepared by mixing the following ingredients, all parts by weight:

Parts Sodium carboxymethyl cellulose 22.0 Sorbitol U.S.P.; 70% 7.0

Water 31.0 Sodium sulfite 33.6 Sodium pyrosulfite 6.4

The crumb is extruded to give soft, pliable, spaghettilike masses. This product is folded or loosely packed into any convenient shape and dried to form a tough, resilient, non-fiable product which may be used in air conditioning 7 A devices operating in air with a relatively humidity of about 40 to about 65% to remove formaldehyde from the air.

EXAMPLE 11 A coarse powder or crumb is preparedby mixing the following ingredients in a ribbon blender:

Parts Water 12.6 Diethyl glycol 9.6 Sodium pyrosulfite 13.7 Sodium sulfite 50.0 Methyl cellulose 14.1

The crumb is extruded in a water-cooled plastics extruder through orifices & inch in diameter to give a product in soft, pliable, spaghetti-like masses. This product is folded or loosely packed into any convenient shape. It is dried to give a product with the following approximate composition:

Parts Methyl cellulose 14.7 Water 7.5 Diethylene glycol 10.0 Sodium salts of sulfurous acid 67.8

This product may be used to absorb formaldehyde from air.

EXAMPLE 12 A crumb mix is prepared by mixing the following ingredients, all parts by weight:

Parts Attapulgite clay 39.0 Sodium pyrosulfite 5.0 Sodium sulfite 20.0 Glycerol 12.0 Water 24.0

limited by this description 8 v or otherwise, except as defined in the appended claims.

That which is claimed is:

1. A solid cohesive composition for removing formaldehyde odors from the air comprising an intimate mixture of a water-soluble salt of sulfurous acid selected from the group consisting of the alkali metal salts and ammonium salts of sulfurous acid, a humectant-for controlling the amount of water in the composition, and a solid hydrophilic binder, said humectant being present in an amount suflicient to ensure the presence of sufiicient water in said composition to maintain said salt partially in solution and thereby suitable for absorbing formaldehyde and to plasticize the hydrophilic binder, said binder being present in an amount suflicient to maintain said intimate mixture cohesive, and said composition having a pH within the range of approximately 6.5 to 9.5.

2. A composition as defined in claim 1 wherein the humectant is selected from the groupof compounds consisting of glycerol, sorbitol, diethylene glycol, and sodium lignosulfonate and wherein the binder is a hydrophilic organic gum.

3. A composition as defined in claim 1 and in which the pH of the composition is within the range of approximately 7 to 8.

4. A composition as defined in claim 1 and in which the sulfurous acid salt is a mixture of a pyrosulfite and a normal sulfite salt.

5. A composition as defined in claim 1 and in which the sulfurous acid salt includes a mixture of a pyrosulfite salt and an inorganic base.

6. A composition as defined in claim 1 and in which the sulfurous acid salt includes a mixture of a normal sulfite salt and an inorganic acid.

7. A composition as defined in claim 1 and having a. spaghetti-like form.

8. A composition as defined in claim 1 and being in flake form.

9. A composition as defined in claim 1 and being in pellet form.

References Cited UNITED STATES PATENTS 2,184,053 12/1939 Mulhler 252-188 2,388,390 11/1945 Cook et al 252194 2,483,418 10/1949 Kamlet 252-494 X 2,825,651 3/1958 Loo et al. 252-188 X LEON D. ROSDOL, Primary Examiner.

M. WEINBLATT, Assistant Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, D.C. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,400,079 September 3, 1968 Alfred T. Clifford et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shmm below:

Column 1, line 66, "inventory" should read invention lines 66 and 67, "previde" should read provide Column 2 line 22 after "in" insert an line 46, "foremaldehyde should read formaldehyde Column 4, line 72, "17.8" should read 13.7 Column 6, line 75, "non-fiable" should read non-friable Column 7, line 9, "Diethyl" should read Diethylene Signed and sealed this 20th day of January 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR

Attesting Officer Commissioner of Patents 

